Aerosol inhalation equipment is often used in medical facilities for generating aerosol mists for diagnostic and therapeutic procedures. Such devices are especially useful in pulmonary therapy for pneumonia and for introducing radioactive vapors for diagnosing diseases.
The engine of most aerosol-generating equipment is the nebulizer, a device which mixes pressurized air or oxygen with diagnostic or therapeutic fluids to create an aerosol mist. During operation, the liquid to be aerosolized is placed in a liquid reservoir in the nebulizer. Air under pressure enters the system and acts to draw the liquid up a delivery tube to an aerosol exit orifice, similar to a jet pump. At the aerosol exit orifice, the fluid is atomized into a fine mist. Larger drops that are produced in the mist impinge on baffles above the aerosol exit orifice where they drain back into the reservoir of the nebulizer. Smaller drops are entrained by the air and are carried through the delivery system to the patient's lungs. A typical nebulizer is disclosed in Bordoni et al., U.S. Pat. No. 4,823,784.
The overall effectiveness of a nebulizer depends largely upon the distribution and size of the droplets produced. Droplets larger than 3.5 micrometers generally do not leave the nebulizer and run back into the bowl to be atomized again. Droplets between about 1.5 and 3.5 micrometers often collect on the walls of the delivery system and frequently settle onto the lips, mouth, or bronchial tubes of the patient without ever reaching the alveolar, often referred to as the "deep lung".
A 1987 study performed on one aerosol inhalation system indicated that only 25% of the liquid initially charged into the nebulizer actually reached the patient's lungs during a seven minute exposure. Typically, only 66% of this amount actually remains in the deep lung of the patient; the other 33% is exhaled. Therefore, only about 16% of the liquid therapeutic or diagnostic substance charged to the nebulizer is ever used by the patient. The remainder is wasted, or winds up contaminating the environment.